Thanks to the prosperous progress of technologies at present time, novel information products are developed and introduced, satisfying the various needs of many people. Early displays are mainly cathode ray tubes (CRTs). Due to their huge size and power consumption as well as radiation production, which is harmful to long-term users of the displays, modern displays in the market are gradually replaced by liquid crystal displays (LCDs). LCDs have the advantages of small size and light weight, low radiation, and low power consumption. Thereby, they have become the mainstream in the market.
In addition, current small-sized TFTLCD driver ICs are developing towards zero-capacitor driving, which means the original external capacitor is now built-in inside the driver IC. The biggest problem of this method is that the required charges for the panel of LCD cannot completely supplied by the built-in capacitor of the IC. For solving this problem, if a charge pump is added to each source driver, the panel can be used as a voltage stabilizing capacitor. The charges required by the panel to supplied to the panel by the charge pump via the operational amplifier (OPA) in the source driver. Nonetheless, this method has a drawback that the static current of the OPA in the source driver cannot be excess, which is approximately less than 1 uA. This is because the charge pump has no stabilizing capacitor for supplying excessive static current. If the OPA in the source driver has to maintain sufficiently small static current, its output stage will face the problem of inability in driving high or driving low voltage. There are many methods to solve this problem, for example, modifying the architecture of OPA to meet the required static current, or using a pre-charge switch and a comparator to achieve the pre-charge function. If the latter method is adopted, because the signal to be compared is the signal of its own highest power supply, the problem of incapability in high gray-scale transition might occur.
Accordingly, the present invention provides a novel start-up circuit, which can prevent the problem of incapability in high gray-scale transition as well as achieving a driving model of low power consumption and fast charging. The problems described can thus be solved.